1. Field of the Invention
The present invention relates to a composition having bacteristatic and bactericidal activity against undesirable bacteria present in food, and to a process for treating food with such a composition in order to render the food more resistant to spoilage and safer for consumption.
2. Description of the Related Art
Processes and compositions for treating food products to prevent or inhibit bacterial spoilage and/or the development of harmful bacteria are widely practiced . It is a common practice in the commercial sterilization of low-acid foods (i.e., pH>4.5) to apply a combination of heat and pressure to canned or pouched foods sufficient to achieve at least a 12 decimal (12D) reduction of spores of Clostridium botulinum, considered the most heat resistant of dangerous bacteria in foods deriving from its ability to form highly heat resistant spores that survive lesser processes. Unfortunately, typical 12D sterilization processes can alter the appearance and flavor of foods, making them less desirable than foods that are processed at temperatures that are less lethal (sublethal) to spores of C. botulinum. 
In recent years, more foods have been subjected to treatment with sublethal doses of heat, pressure, irradiation, ultrasound, or combinations thereof, which can decrease bacterial levels of a food product while also providing for a more organoleptically attractive food product. These sublethal processing treatments alter food products less dramatically than traditional 12D heat treatments used to sterilize food products, but most foods processed in this fashion must then be refrigerated to protect against the possible outgrowth of sporeforming bacteria.
While sublethal processing treatments kill most vegetative spoilage and pathogenic bacterial cells, they typically kill only a fraction of potential bacterial spores, which have elevated resistance to heat, irradiation and other treatments. Such spores can survive sublethal processing treatments and subsequently grow in the processed food, causing spoilage, illness and, in the worst cases, death. For this reason, most foods treated in this fashion are refrigerated so as to slow or prevent the growth of such spores.
Food products infected with these spore-forming bacteria are numerous and include, but are not limited to, ready to eat meals and entrees, deli salads, dairy foods, dressings and condiments, processed or cured meats, poultry, and seafood, as well as processed fruits and vegetables, fruit and vegetable derived products, grains and grain derived products, pastas, soups, and aseptically packaged foods. The long refrigerated shelf-life of ready to eat foods, especially vacuum packed, modified atmosphere packed (MAP), and canned food products, can be especially troublesome as it may allow the spores of some bacteria, such as Clostridium botulinum, to germinate and grow in the food with the production of lethal toxins. Such risk may be higher in sublethally processed foods because sublethal processes typically destroy the nonpathogenic vegetative species of bacteria that would otherwise spoil or compete with sporeforming species. A further exacerbating risk in this class of foods is the use of vacuum or modified atmosphere packaging processes, which produce the anaerobic conditions necessary for the development and growth of clostridial spores.
Extensive research has also been conducted in the field of food safety to develop food grade compositions which can function as antibacterial agents. Relevant prior art may be found in U.S. Pat. Nos. 5,096,718 and 5,260,061 and the references cited therein. These patents disclose the use of metabolites of propionic acid bacteria in certain foods to increase the shelf life of the resulting products. These metabolites demonstrate efficacy against gram negative bacteria but are typically not as effective against gram positive bacteria or their spores.
JP 07-115950 discloses the combination of bacteriocins produced by lactic acid bacteria of the propionibacteria genus in combination with either organic acids and their salts, fatty acid esters of polyhydric alcohols, amino acids, antibacterial peptides and proteins, polysaccharides comprising sugars, saccharic acids and amino sugars and their partial decomposition products, spices and their essential oils and plant components, and alcohols.
U.S. Pat. No. 5,217,250 discloses the use of nisin compositions as bactericides. Nisin is a lantibiotic, more specifically, a polypeptide with antimicrobial properties which is produced in nature by various strains of the bacterium Streptococcus lactis. Nisin is primarily effective against gram positive bacteria. This patent discloses that the combination of a chelating agent, such as EDTA or other acetate salts or citrate salts, with nisin can result in a broad range bactericide.
U.S. Pat. No. 5,458,876 discloses the combination of a lantibiotic with lysozyme as an antibacterial composition.
EP 0 466 244 discloses a composition having improved antibacterial properties which is a mixture of at least one of each of the following groups of compounds: (I) a cell wall lysing substance or a salt thereof, (II) an antibacterial compound, and (III) an adjuvant selected from organic acids acceptable for use in food products, preparations for cosmetic use or personal hygiene, or salts of these acids; phosphates and condensed phosphates or their corresponding acids; and other sequestering agents. Preferably (I) is lysozyme, (II) may be a bacteriocin (e.g. nisin or pediocin), and (III) may be acetic acid, lactic acid, citric acid, propionic acid, tartaric acid, orthophosphates, hexametaphosphates, tripolyphosphates, other polyphosphates, or sequestering agents containing substituted or non-substituted amino groups, e.g. EDTA.
EP 0 453 860 discloses the combination of nisin with a phosphate buffer effective at a pH of between 5.5 and 6.5 to help eradicate gram negative bacteria from surfaces.
U.S. Pat. No. 5,989,612 discloses the combination of a propionibacterial metabolite, not solely propionic acid, with a potentiator substance, which includes chelators, essential oils, or organic acids (other than propionic acid, acetic acid, lactic acid, and their respective salts).
U.S. Pat. No. 6,207,210 discloses the combination of a propionibacterial metabolite, not solely propionic acid, a lantibiotic, and one or more phosphate salts which act as a chelating agent.
It would still be beneficial to develop an antibacterial composition effective against both gram positive and gram negative bacteria, as well as against gram positive spores, especially in foods subjected to a sublethal (less than 12D) processing treatment.